Results 1 to 11 of 11
  1. #1

    Whistling Return Duct

    I recently had an air-conditioning system installed in a house I’m building and have a problem with a whistling noise in the return duct. The installer was notified and his employees attempted to correct the problem by installing an additional, smaller return duct in my office which is located near the larger return. This reduced, but did not eliminate the noise which gets louder if the office door is closed. Some men working on the house overheard the AC dealer’s employees discussing installing a baffle inside the main return to quiet the noise by restricting airflow. I believe that this would result in the system having to run longer to attain the same level of heating/cooling which would result in an increase in my heating & cooling costs. Can anyone suggest a solution to this problem? I personally think a bigger main return is the answer, but want to see what other people think

  2. #2
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,371
    What is the tonnage of the HVAC system? It's possible you have an undersized duct system /oversized HVAC system. Was a load calculation done? Adding returns may alleviate the issue a bit, but a balanced and correctly sized HVAC/duct system is needed.

  3. #3
    Join Date
    Nov 2007
    Location
    Sherman, TX
    Posts
    9,441

    Lack of Return Air

    one of the most common system problems I run into is lack of adequate return air. I frequently run into 3 1/2 to 4 ton systems with a single 14 inch return. You can't have "too much" return air.

    At least once a month, I find a blower wheel in a relatively new system that the center pan has ripped loose from the fins.....almost always caused by inadequate return air ducting.

    Depending on your style of filter/return grill, you might also try bending the fins to a steeper pitch, as return grill fins can restrict the opening as much as 1/3.

  4. #4
    Thanks for the quick reply!! It's a 3-ton system. The dealer stated he would be using Manual J when we talked in his office (I think that's what is used to size systems) and I remember him looking at the bluprints for the house and counting up how many windows faced in each direction. I don't remember what else he may have noted (this was in April). His quote states that "Ducting will be designed according to the standards and specifications found in ACCA (Air Conditioning Contractors of America) manual D, G, & T".

  5. #5
    Join Date
    Nov 2007
    Location
    Sherman, TX
    Posts
    9,441

    at the risk of being pilloried

    Sometimes, I fear that too many folks get so wrapped up in "calculations", that common sense and experience get lost in the shuffle.

    Keep in mind, that many of us have service jobs in the field, because somebody's "calculations" didn't work in real-life application.

  6. #6
    Join Date
    May 2007
    Location
    DC Metro Area (MD)
    Posts
    3,371
    JohnPlenge,

    What is your return air setup? Small/Large returns on each floor, etc. From what you say about the door being closed or opened along with the whisting, it sounds like an imbalanced and/or undersized duct system. You should consider having the contractor over to listen to it himself. Remember, duct systems aren't going to be silent (I'm not sure if this is your first experience with forced air systems; I doubt it).

  7. #7
    Join Date
    Aug 2002
    Location
    Office and warehouse in both Crystal River & New Port Richey ,FL
    Posts
    18,836
    Quote Originally Posted by JohnPlenge View Post
    Thanks for the quick reply!! It's a 3-ton system. The dealer stated he would be using Manual J when we talked in his office (I think that's what is used to size systems) and I remember him looking at the bluprints for the house and counting up how many windows faced in each direction. I don't remember what else he may have noted (this was in April). His quote states that "Ducting will be designed according to the standards and specifications found in ACCA (Air Conditioning Contractors of America) manual D, G, & T".
    Your on the right track if they can do what they state!!!!

    Calculation ,done correctly ,works every time!!!
    Last edited by dash; 11-06-2007 at 09:34 AM.

  8. #8
    Join Date
    Jun 2000
    Location
    WYO
    Posts
    2,019
    A whistling sound can be caused by a simple reed effect from a blower door not sealing right from a properly sized system. Undersized return can make it worse tho. Is your filter dirty?
    never say never

  9. #9
    Join Date
    Jun 2007
    Location
    Metro St. Louis
    Posts
    181
    Quote Originally Posted by RyanHughes View Post
    ...
    Remember, duct systems aren't going to be silent (I'm not sure if this is your first experience with forced air systems; I doubt it).
    ...
    Hehe... mine's silent (at least on first stage). The only way I can tell if it's running is if I hear the vibration of the heat pump itself. And if I can get rid of that....

    I'll know more after tonight when the system will have to run in second stage quite a bit (low of 25* tonight). I expect to hear some airflow - but only noticable in the dead of the night.

  10. #10
    Join Date
    Oct 2007
    Posts
    226
    Quote Originally Posted by JohnPlenge View Post
    Thanks for the quick reply!! It's a 3-ton system. The dealer stated he would be using Manual J when we talked in his office (I think that's what is used to size systems) and I remember him looking at the bluprints for the house and counting up how many windows faced in each direction. I don't remember what else he may have noted (this was in April). His quote states that "Ducting will be designed according to the standards and specifications found in ACCA (Air Conditioning Contractors of America) manual D, G, & T".
    Sounds like he did it right but I suppose that all could have been to impress you and get the job, I hope not.

  11. #11
    Thanks everyone for the replies. I’ll try to answer all your questions in my reply. The original return air setup consists of a large return duct near the guest bedroom doorway and a smaller return in the master bedroom (on the opposite side of the house). When I complained about the whistling, a third return was installed inside the office which is next to the guest bedrooms.

    This isn’t my first experience with a forced air system, but I’ve never heard this sound before in any house. This is my first experience with a return system of this type consisting of one or more ducts carrying air back to the unit. All the others I’ve dealt with had what I would guess is the older way of doing things – the unit in a small closet with two rectangular openings in the bottom of the wall to allow return air to flow to the unit.

    Can someone tell me a good way to check the seal on the blower door? I guess feeling for leaking air would work. I’m cleaning the filter every 2-3 days while the house is being finished so that shouldn’t be a problem. I hope he wasn’t simply trying to impress me, he came very highly recommended by several coworkers.

    I am concerned about the baffle one of the construction workers overheard the installer talking about. This sounds like something that would be placed inside the return duct to eliminate the sound by restricting airflow. I’m concerned that this would reduce the efficiency of the system by making it run longer to achieve the same level of heating/cooling and might cause premature wear by making the system work harder. Can someone give me some information on this?

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event